This application discloses an improved limp home feature for an electronic throttle control.
An electronic throttle control (ETC) replaces the mechanical throttle linkage to control the position of the throttle valve. The throttle valve actuated by the ETC is opened proportionally according to signals received from a sensor placed on an accelerator pedal. The ETC opens the throttle valve proportionally to movement of the accelerator pedal.
A typical ETC will be mounted to a throttle body. The throttle body includes an airflow passage though which air is brought into the engine. The throttle valve is disposed within the airflow passage and attached to a shaft for rotation about an axis to regulate the intake of air. A closed throttle position is set to provide a minimum airflow requirement for an engine, to keep an engine at or near a stall condition.
A limp home throttle position is set for when the ETC is disabled, and provides an engine speed that will produce enough power that can easily be controlled by a driver. The intent of the limp home throttle valve position is to provide the driver with sufficient power to maneuver the vehicle.
Current mechanisms for attaining the limp home throttle valve position include double spring arrangements that are balanced against each other to provide the proper throttle valve position upon disablement of the ETC. The double spring arrangement typically includes one spring to close the throttle valve acting against another spring to open the throttle valve to the limp home throttle valve position. The double spring arrangement must be carefully balanced to attain the desired amount of throttle valve opening for the limp home position. Further, the use of opposing springs creates an inconsistent limp home throttle position because the balance between the springs may change over time. The limp home position must be set precisely, because a limp home engine speed that is too low will not provide the necessary engine power to maneuver the vehicle. Alternatively, too high an engine speed may create a sensation in the driver of being out of control of the vehicle.
For these reasons it is desirable and necessary to provide a simple mechanism that provides for reliable setting and preservation of the limp home throttle valve position for an ETC.
The subject invention is an electronic throttle control with a linkage assembly that provides for the setting of a limp home throttle valve position. Essentially, the subject invention eliminates the double spring arrangement of the prior art by providing a self-closing throttle valve.
The throttle valve includes an airfoil shape utilizing the flow of air through the throttle body to produce a closing force, thereby eliminating the need for a throttle return spring. The throttle valve also includes differential areas that create a net force that rotates the throttle valve towards the closed position. The throttle valve arrangement allows a precise amount of throttle movement from a closed throttle position to the limp home throttle position when the ETC motor is disabled. A throttle valve is attached to a shaft within the airflow passage and rotates about an axis to regulate air intake. An electric motor drives a lever rigidly attached to the shaft through a linkage assembly. A biasing member attached to the shaft biases the throttle valve toward the closed position when the throttle valve is at or near the open position. A second biasing member attached to the sector gear biases the throttle valve to a limp home position when the electric motor is disabled.
The subject invention overcomes the deficiencies of the prior art by providing a simple, reliable and cost effective linkage assembly that provides for the ETC limp home throttle positions.